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The antagonistic regulation of abscisic acid‐inhibited root growth by brassinosteroids is partially mediated via direct suppression of ABSCISIC ACID INSENSITIVE 5 expression by BRASSINAZOLE RESISTANT 1

Yang, Xiaorui, Bai, Yang, Shang, Jianxiu, Xin, Ruijiao, Tang, Wenqiang
Plant, cell and environment 2016 v.39 no.9 pp. 1994-2003
abscisic acid, brassinosteroids, gene expression, genes, growth and development, hormones, mutants, root growth, sequence analysis, signal transduction, transcription factors
Brassinosteroids (BRs) and abscisic acid (ABA) are plant hormones that antagonistically regulate many aspects of plant growth and development; however, the mechanisms that regulate the crosstalk of these two hormones are still not well understood. BRs regulate plant growth and development by activating BRASSINAZOLE RESISTANT 1 (BZR1) family transcription factors. Here we show that the crosstalk between BRs and ABA signalling is partially mediated by BZR1 regulated gene expression. bzr1‐1D is a dominant mutant with enhanced BR signalling; our results showed that bzr1‐1D mutant is less sensitive to ABA‐inhibited primary root growth. By RNA sequencing, a subset of BZR1 regulated ABA‐responsive root genes were identified. Of these genes, the expression of a major ABA signalling component ABA INSENSITIVE 5 (ABI5) was found to be suppressed by BR and by BZR1. Additional evidences showed that BZR1 could bind strongly with several G‐box cis‐elements in the promoter of ABI5, suppress the expression of ABI5 and make plants less sensitive to ABA. Our study demonstrated that ABI5 is a direct target gene of BZR1, and modulating the expression of ABI5 by BZR1 plays important roles in regulating the crosstalk between the BR and ABA signalling pathways.